For reconstruction of anal function in fecally incontinent patients, it may be feasible to transpose the gracilis muscle around the analcanal, using electrical stimulation to trigger contraction. However, because the fast-twitching gracilis muscle is incapable of prolonged contraction without fatigue, it is necessary to convert it to a slow-twitching, fatigue-resistant muscle. When the muscle contraction decreases even transiently between stimuli, the neoanus cannot maintain continence. Thus, the muscle must keep some tension between each stimulus. To fulfilll these criteria, the neoanal sphincter must be stimulated at a frequency that can include sufficient summation. We demonstrated this conversion and contractile summation by long-term electrical pulse stimulation (0.2 msec pulse width) at low frequencies using a rabbit model. The nerve to the gracilis muscle of rabbits was continuously stimulated at 2 Hz, 5 Hz and 10 Hz for 2 to 8 weeks. This conditioning reduced frequency necessar
… Morey for summation, and the muscles conditioned at 10 Hz for 6 or 8 weeks induced sufficient summation (fusion index>90%) at 20 Hz, and also showed sufficient summation (fusion index=80%) at 15 Hz, a frequency that produced muscle contraction without fatigue. The conditioning also prolonged twitch contraction time and half relaxation time for one-shot pulse stimulation, but the twitch contraction speed reduced with conditioning at a frequency more than 5 Hz. In the 6-week conditioning group, the percentage of type I fibers, identified by ATPase staining method, increased as the conditioning frequency became higher and the conditioning period became longer. After assessment on the conversion of gracilis musle to a fatigue-resistant muscle, transposition of the muscle around the rectum was performed in Japanese white male rabbits. The muscles conditioned at 10Hz for 6 weeks were stimulated at 15 Hz, a low frequency to permit prolonged contraction, and the neoanal pressure increased maximally to more than 100 cmH2O.The pressure suitable for fecal continence maintained in long period more than 10 weeks (maximally 38 weeks) without any trouble, while the non-conditioning group showed decay of neoanal pressure in short period. The conditioning made it possible for the rabbit's gracilis muscle to create anal pressure at a frequency permitting prolonged contraction. Thus, we concleded that the conditioning at 10 Hz for 6 weeks can convert rabbit gracilis muscle to a slow-twitching, fatigue-resistant muscle and produce enough summation at a low frewuency stimulation to permit prolonged contraction suitable for power source to reconstruct a neoanal sphincter. Less